A conventional engine of this type has, inside a stationary casing, a rotary group of pistons comprising an inner rotor of stacked ring disks to each of which a radial vane is rigidly attached. An outer ring is provided with arcuate members separated by fulcrum slides which guide the vanes whose tips sealingly graze the inner casing wall. This is disadvantageous in view of thermal expansion and is also cause for rapid deterioration even at moderate speeds, necessitating large maintenance and repair expenditures. Another drawback of the conventional engine is that boosting is effected in a system of inner ring chambers, whereas compressing takes place in an outer group of chambers. Though this arrangement would seem to facilitate cooling, its volume conditions entail the stiff price of rather poor compression and thus low overall efficiency. The power-to-weight ratio is relatively small, too.
Other prior art internal combustion engines of somewhat similar types feature a crank mechanism or eccentric shaft borne in a stationary casing. A rotor is provided with chambers defined by vanes which are moved, by the eccentric mechanism, both radially and shuttlewise in slit guides. The oscillatory movement of such a rotary piston array produces compression much like a cylindrical piston, although additional angular motions occur. These designs are, however, quite prone to trouble in respect of sealing as well as wear and tear. Most harmful is the vibratory flyweight due to large unbalanced masses going to and fro.